Defective memory cells in a semiconductor device can compromise the functionality of a semiconductor device, in particular a memory device, resulting in a defective product. To improve production yields, semiconductor memory devices are manufactured with redundant memory cells. When defective memory cells are detected, they may be replaced by the redundant cells.
Redundant memory cell sectors include redundant rows and columns which can be used to replace rows and columns which include defective cells. For example, when a defective memory cell is detected through a test after fabrication, a program operation, which replaces an address of the defective memory cell with an address of the redundancy cell, is performed in an internal circuit. Therefore, when an address signal corresponding to a defective line is input in actual use of the semiconductor memory apparatus, the redundant line is accessed other than the defective line.
Conventional repair methods use fuse operations. Since repairing a semiconductor device using a fuse operation is performed at a wafer level, the method cannot applied be when a defective cell is detected after the device is packaged. Therefore, an antifuse method is used to replace cells after packaging.
In general, an antifuse has an electric characteristic opposite to a fuse. That is, the antifuse device is generally a resistive fuse device which has high resistance in an initial state and low resistance after a programming operation. An antifuse may use a very thin dielectric material such as silicon oxide (SiO2), silicon nitride, tantalum oxide, or silicon dioxide—silicon nitride—silicon dioxide (ONO) interposed between two conductors.
The programming operation of the antifuse device includes breaking down the dielectric between the two conductors by applying a high voltage through antifuse terminals for a sufficient period of time. Therefore, when the antifuse is programmed, the conductor at both edges of the antifuse is short-circuited so that the antifuse has a low resistance. Therefore, the antifuse is electrically open in a normal state and electrically short-circuited in a programmed state by applying a high voltage.
For example, an antifuse may include a gate formed on a gate insulating layer, a contact plug formed to be spaced from the gate at a fixed distance, and a conductive interconnection connected to a top of the contact plug, and is programmed by breaking down the gate insulating layer by applying a high voltage between the gate and the contact plug.
When a gate insulating layer provided in an edge of an active region is broken down in an antifuse programming operation, an interface between the semiconductor device and the gate may become reoxidized in subsequent thermal processes, reducing the reliability of the antifuse operation.
Furthermore, when a gate size is increased to improve reliability and stability of the antifuse, a corresponding antifuse area is also increased, reducing productivity of a net die.